Final answer:
Tertiary follicles, consisting of an antrum, theca externa, theca interna, oocyte, and granulosa cells, are the mature forms of ovarian follicles ready for ovulation.
Step-by-step explanation:
Structures that consist of an antrum, theca externa, theca interna, oocyte, and many granulosa cells are known as tertiary follicles or antral follicles. Tertiary follicles contain a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum, which is a fluid-filled cavity that forms within the follicle during the later stages of folliculogenesis. These follicles experience significant growth thanks to the proliferation of granulosa cells, the development of theca cells, which work with granulosa cells to produce estrogens, and the accumulation of follicular fluid in the antrum. During the ovulatory phase, the dominant follicle releases the oocyte, now surrounded by granulosa cells, into the peritoneal cavity, a process known as ovulation.